CN112310974B - Neutral point small reactance value-taking method of magnetic control type controllable reactor - Google Patents

Neutral point small reactance value-taking method of magnetic control type controllable reactor Download PDF

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CN112310974B
CN112310974B CN201910709345.7A CN201910709345A CN112310974B CN 112310974 B CN112310974 B CN 112310974B CN 201910709345 A CN201910709345 A CN 201910709345A CN 112310974 B CN112310974 B CN 112310974B
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neutral point
value
small
reactance
small reactance
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钟高跃
石祥建
韩兵
吴龙
韩焦
牟伟
刘为群
潘仁秋
苏家财
王梓锐
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NR Electric Co Ltd
NR Engineering Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1864—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein the stepless control of reactive power is obtained by at least one reactive element connected in series with a semiconductor switch
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1871—Methods for planning installation of shunt reactive power compensators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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Abstract

The invention discloses a method for dereferencing a neutral point small reactance of a magnetic control type controllable reactor, which comprises the following steps: step 1, providing a voltage expression at a phase-lacking position of a three-phase power transmission line with a magnetic control type controllable reactor; step 2, aiming at the purpose of small value of the open-phase voltage, calculating the value range of the small reactance of the neutral point according to the following principle: firstly, the small reactance value of the neutral point makes the voltage expression far away from the singular point; secondly, the small reactance value of the neutral point enables the voltage expression coefficient to be-1; and 3, selecting a plurality of small reactance values in the value range obtained in the step 2, and determining the small reactance value of the neutral point according to specific requirements. The small reactance value method can select the small reactance value of the neutral point strictly following the circuit and magnetic circuit law, and the calculation method is simple and practical.

Description

Neutral point small reactance value-taking method of magnetic control type controllable reactor
Technical Field
The invention belongs to the field of a neutral point small reactance selection method of a reactor in a high-voltage alternating-current power grid, and particularly relates to a neutral point small reactance selection method for a magnetic control type controllable reactor.
Background
When the extra-high voltage alternating current circuit is in light load or no-load operation, the charging power is very high, and a shunt reactor is required to be arranged on the circuit for suppressing overvoltage. For an ultra/extra-high voltage transmission line with a shunt reactor, after circuit breakers at two ends of a fault phase are tripped, the tripped fault phase generates larger overvoltage under the action of capacitive coupling and electromagnetic coupling between a non-fault phase and the fault phase. The small reactance connected to the star-connected parallel reactor neutral point plays a key role in eliminating power frequency resonance phenomena under the non-full-phase state, so that the parallel reactor with the small reactance having the neutral point is already the characteristic of the existing ultra-high voltage and above voltage level power transmission system, as shown in fig. 1. The value method of the neutral point small reactance with fixed high reactance is mature and is widely applied to field practice, wherein the value of the neutral point small reactance is selected according to the approximate full compensation design of the interphase capacitance.
The magnetic control type controllable reactor is completely different from the traditional fixed high-impedance reactor: firstly, the reactive power value generated by the magnetic control type controllable reactor under a certain voltage is fixed for fixed high impedance and can be continuously adjusted for the reactive power of the magnetic control type controllable reactor due to the difference of the capacity; secondly, the two structures are different, and the magnetic control type controllable reactor comprises a net side winding, a control winding and a compensation winding, as shown in fig. 2. The grid side winding is directly connected with a power grid and is an output end of reactive power; exciting current flows through the control winding to adjust the magnitude of output reactive power; the compensation winding is generally in an angle joint and used as a self-excitation power supply, and the principle of the compensation winding is that the saturation degree of a magnetic circuit is changed by changing the direct current of the control winding, so that the current on the network side is changed to realize reactive power regulation. The fixed high impedance is usually only the net side winding. The two differences make the traditional method for fixing high reactance and selecting neutral point small reactance completely unsuitable for the magnetic control type controllable reactor, and in addition, because the capacity of the magnetic control type controllable reactor can be continuously adjusted and the characteristics of a compensation winding exist, the input parameter of the neutral point small reactance value of the solver is changed, and the method for solving the value is more complex. In the prior art, a magnetic control type controllable reactor is rarely used for a power transmission line and is usually used on a bus, so that a small reactance with a neutral point is not required to be added. At present, some countries in China, China in China and Africa use the magnetic control type controllable reactor as a high-impedance line, so that the working condition that the magnetic control type controllable reactor is hung on a phase-lacking line exists, and the situation that a small reactance with a neutral point is additionally arranged needs to be considered. At present, the value of the small inductance of the neutral point of the magnetic control type controllable reactor is hardly researched, and the problem is solved by the invention.
Disclosure of Invention
The invention aims to provide a method for dereferencing the neutral point small reactance of a magnetic control type controllable reactor, which can select the neutral point small reactance strictly following the law of a circuit and a magnetic circuit and has simple and practical calculation method.
In order to achieve the above purpose, the solution of the invention is:
a neutral point small reactance value taking method of a magnetic control type controllable reactor comprises the following steps:
step 1, providing a voltage expression at a phase-lacking position of a three-phase power transmission line with a magnetic control type controllable reactor;
step 2, calculating the value range of the small reactance of the neutral point according to the following principle by taking the small value of the open-phase voltage as the purpose: firstly, the small reactance value of the neutral point makes the voltage expression far away from the singularity; secondly, the small reactance value of the neutral point enables the voltage expression coefficient to be-1;
and 3, selecting a plurality of small reactance values in the value range obtained in the step 2, and determining the small reactance value of the neutral point according to specific requirements.
In the step 1, the voltage expression at the phase-lacking position of the three-phase power transmission line with the magnetic control type controllable reactor is as follows:
Figure BDA0002153186650000021
wherein, EaThe power grid rated voltage is adopted, and omega is the power frequency angular frequency; c0Being a capacitance to ground, CmIs an interphase capacitor; x1σCorresponding inductance value L for the side leakage reactance of the reactor network1σ；XμFor exciting impedance, corresponding to inductance value Lμ；XnA small reactance of neutral point corresponding to inductance value Ln。
In step 2, the voltage expression is made to satisfy the small reactance value of the neutral pointExpression for avoiding phase failure, i.e. for keeping away from singularities
Figure BDA0002153186650000022
The denominator of (c) is zero, let:
Figure BDA0002153186650000031
solve to obtain a small reactance L of a neutral pointnAnd LμIs a function ofn＝f1(Lμ) The following are:
Figure BDA0002153186650000032
Lμis substituted into the above formula to obtain LnA value; these calculated values are avoided when selecting the neutral point.
In the step 2, in order to satisfy the condition that the reactance value of the neutral point is small and the coefficient of the voltage expression is-1, the voltage in the voltage expression is made to be the voltage
Figure BDA0002153186650000033
The coefficient of the front is K:
Figure BDA0002153186650000034
solve out the small reactance L of the neutral pointnAnd LμIs a function of the relation Ln＝f2(Lμ) The following are:
Figure BDA0002153186650000035
let K be-1, L in the above formulaμFrom minimum sensitivity to infinity, at LμWithin the variation range of (2), L is calculatednThe value is obtained.
In the step 3, after selecting a plurality of small reactance values, the final small reactance value of the neutral point is determined by considering the manufacturing cost factors of making the absolute value of K small and the small reactance of the neutral point.
After the scheme is adopted, the neutral point selection method of the magnetic control type reactor is obtained from the angle of the open-phase overvoltage analytic expression, the difficulty of selecting the neutral point small reactance due to variable capacity and complex structure of the magnetic control type reactor is overcome, the method can be applied to an actual power grid, and a basic technical support is provided for researching the transient and steady processes of the magnetic control type reactor and the influence of the transient and steady processes on the power grid.
Drawings
Fig. 1 is a schematic diagram of a power transmission line with a shunt reactor according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a three-phase magnetically controlled reactor according to an embodiment of the present invention;
fig. 3 is an equivalent circuit diagram for calculating phase-lacking overvoltage according to the embodiment of the present invention;
FIG. 4 shows a function L provided by an embodiment of the present inventionn＝f1(Lμ) Graph of (a);
FIG. 5 is a diagram of a function L provided by an embodiment of the present inventionn＝f2(Lμ) Graph of (a).
Detailed Description
The technical scheme and the beneficial effects of the invention are explained in detail in the following with the accompanying drawings.
Fig. 2 is a schematic structural diagram of a three-phase magnetically controlled reactor provided in an embodiment of the present invention, in which a reactor body is a three-phase octal-type structure, and a grid-side winding is directly connected to a power grid to provide reactive power to the power grid; the control winding is connected with an excitation power supply (a rectifying device in the figure) and is used for adjusting the magnitude of the reactive power output by the network side; the compensation winding is connected with the high-voltage side of the excitation transformer to provide power for an excitation system, so that the self-excitation system is formed.
The head and the tail of a certain 400kV power transmission line are respectively provided with a controllable high impedance, the rated capacity of each power transmission line is 40MVar, the rated voltage is 400kV, and the rated frequency is 50 Hz; the equivalent circuit diagram after phase failure is shown in FIG. 3, in which Eb,EcIs the equivalent of a healthy phaseA voltage source;
Figure BDA0002153186650000041
the current is the current of a network side winding of the reactor;
Figure BDA0002153186650000042
compensating the winding current for the reactor;
Figure BDA0002153186650000043
is the voltage at the phase loss.
If the maximum capacity which can be generated by the reactor is 1.2 times of rated capacity, the corresponding minimum impedance is 3333.3 ohms, namely 10.6H; network side leakage reactance inductor L1σ3.688H, so the exciting reactance LμThe theoretical value of the variation range is (10.6-3.688, + ∞), i.e., (6.9, + ∞); line-to-ground capacitance C0Value of 1.56uF, interphase capacitance CmThe value was 0.302 uF. For a line with controllable high impedance at two ends of the line, the equivalent expression is that all capacitance values of the original expression are reduced by half, namely, the expression of the A phase voltage is as follows:
Figure BDA0002153186650000044
wherein E isaThe power grid rated voltage is adopted, and omega is the power frequency angular frequency; c0Is capacitance to ground, CmIs an interphase capacitor; x1σCorresponding inductance value L for the side leakage reactance of the reactor network1σ；XμFor exciting impedance, corresponding to inductance value Lμ；XnA small reactance at neutral point and corresponding inductance value Ln(ii) a Among the above parameters, LnIs the quantity to be solved, LμThe change with the change of the excitation current is an independent variable.
First, the expression of avoiding phase-defect voltage should be considered
Figure BDA0002153186650000051
The denominator of (a) is zero, let:
Figure BDA0002153186650000052
solve to obtain the small reactance L of the neutral pointnAnd LμIs a function of the relation Ln＝f1(Lμ) The following:
Figure BDA0002153186650000053
Lμis changed from the minimum inductance value to infinity (the minimum inductance value is the time when the applied exciting current is maximum), and is substituted into the formula to obtain LnThe value is obtained. When selecting a neutral point, the value is avoided. This is the first consideration.
By exciting reactance LμIs X-axis, and has small reactance L at neutral pointnFor the Y axis, find the function Ln＝f1(Lμ) The relationship of (2) is shown in FIG. 4. Known as LμThe minimum value of (2) is 6.9H, and as can be seen from the figure, if the value of the small reactance of the neutral point is greater than and is far away from 1.3H to a certain extent, the voltage denominator expression cannot be zero when the magnetic control high reactance full capacity range is operated.
Secondly, let the voltage in the voltage expression
Figure BDA0002153186650000054
The coefficient of the front is K:
Figure BDA0002153186650000055
solve out the small reactance L of the neutral pointnAnd LμIs a function of the relation Ln＝f2(Lμ) The following are:
Figure BDA0002153186650000056
let K be-1 in the above formula, in LμWithin a variation of (D), to obtain LnThe value is obtained. This is the second consideration.
By exciting reactance LμIs an X-axis, a small reactance L of a neutral pointnFor the Y axis, find the function Ln＝f2(Lμ) The relationship of (2) is shown in FIG. 5. Known as LμThe minimum value of (2) is 6.9H, and the figure shows that when the small reactance of the neutral point is 2.5H, large open-phase overvoltage can not occur under the full capacity.
Finally, according to the function Ln＝f1(Lμ) And Ln＝f2(Lμ) And obtaining the value range of the neutral point small reactance. Selecting a plurality of proper L according to the manufacturing specification of the reactornValue, and then obtaining different L according to the expression of KnAnd the small reactance value of the neutral point is selected to ensure that the absolute value of K is smaller.
Investigating the small reactance L of the neutral pointnOvervoltage conditions when taking values of 1.5H, 2.0H, 2.5H, 3H, respectively. These values are respectively substituted into the following formulas:
Figure BDA0002153186650000061
through comparison, the larger the neutral point small reactance value is, the smaller the overvoltage multiple is in the 4 values.
In consideration of the manufacturing cost of the small reactance in the neutral point, it is preferable to take 2.5H as a whole.
The method for evaluating the small reactance of the neutral point of the magnetically controlled reactor provided by the embodiment of the invention strictly follows the circuit and magnetic circuit law, the excitation impedances of three phases are considered to be the same in calculation, all deductions are started from the premise that the open-phase overvoltage is close to the rated voltage amplitude, and the premise is satisfied by calculating the small reactance value of the selected neutral point, so that a closed-loop processing idea is formed. The calculation method is simple and practical, and can be easily used in engineering practice.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.

Claims (2)

1. A neutral point small reactance value taking method of a magnetic control type controllable reactor is characterized by comprising the following steps:
step 1, providing a voltage expression at a phase-lacking position of a three-phase power transmission line with a magnetic control type controllable reactor;
step 2, calculating the value range of the small reactance of the neutral point according to the following principle: firstly, the small reactance value of the neutral point makes the voltage expression far away from the singularity; secondly, the small reactance value of the neutral point enables the voltage expression coefficient to be-1;
step 3, selecting a plurality of small reactance values in the value range obtained in the step 2, and determining the small reactance value of the neutral point according to specific requirements;
in the step 1, the voltage expression at the phase-lacking position of the three-phase power transmission line with the magnetic control type controllable reactor is as follows:
Figure FDA0003661622220000011
wherein, EaThe power grid rated voltage is adopted, and omega is the power frequency angular frequency; c0Is capacitance to ground, CmIs an interphase capacitor; x1σCorresponding inductance value L for the side leakage reactance of the reactor network1σ；XμFor exciting impedance, corresponding to inductance value Lμ；XnA small reactance of neutral point corresponding to inductance value Ln；
In the step 2, in order to satisfy the small reactance value of the neutral point, the voltage expression is far away from the singularity, that is, the phase-lacking voltage expression is avoided
Figure FDA0003661622220000012
The denominator of (c) is zero, let:
Figure FDA0003661622220000013
get neutral point small electricityanti-LnAnd LμIs a function ofn＝f1(Lμ) The following are:
Figure FDA0003661622220000014
Lμis substituted into the above formula to obtain LnA value; avoiding these calculated values when selecting the neutral point;
in the step 2, in order to satisfy the condition that the reactance value of the neutral point is small and the coefficient of the voltage expression is-1, the voltage in the voltage expression is made to be the voltage
Figure FDA0003661622220000021
The coefficient of the front is K:
Figure FDA0003661622220000022
solve out the small reactance L of the neutral pointnAnd LμIs a function of the relation Ln＝f2(Lμ) The following are:
Figure FDA0003661622220000023
let K be-1, L in the above formulaμRange from a minimum sensitivity value to infinity at LμWithin the variation range of (3), L is calculatednThe value is obtained.
2. The method for dereferencing the small neutral point reactance of the magnetically controlled reactor as claimed in claim 1, characterized in that: in the step 3, after selecting a plurality of small reactance values, the final small reactance value of the neutral point is determined by considering the manufacturing cost factors of making the absolute value of K small and the small reactance of the neutral point.
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